The patient dose should be measured by a suitable radioactivity calibration system immediately prior to administration.

The specific activity should be not less than 370 megabecquerels (10 millicuries) per mg [0.37 megabequerels (10 microcuries) per µg] of Sodium Chromate at the time of use.

It is essential that the user adhere to strict aseptic procedures during the preparation, withdrawal and administration of the labeled red blood cells. Waterproof gloves are to be worn during the labeling procedure to prevent the possibility of radioactive contamination of the hands. Shielded syringes should be used when adding the Chromitope Sodium to the reaction vial and for the withdrawal and administration of the labeled red blood cells. To maintain adequate shielding during the life of the labeled preparation, a lead vial shield and lead cover must remain in place on the reaction vial.

Red Blood Cell Labeling Procedure

Labeling may be performed without washing or centrifugation steps directly in the silicone-coated reaction vial of Bracco A-C-D Solution Modified.*

A 30 to 50 mL sample of whole blood is withdrawn from the patient and added aseptically to a vial of Bracco A-C-D Solution Modified. 1.85 to 5.55 megabecquerels (50 to 150 microcuries) of Chromitope Sodium (Sodium Chromate Cr 51 Injection USP) is then injected into the reaction vial using a shielded syringe. The amount of radioactivity added to the vial will depend on the intended use of the labeled red blood cells. The suspension is incubated for 30 to 60 minutes at room temperature with frequent gentle agitation. After incubation, 100 mg Ascorbic Acid Injection USP is injected into the vial. The ascorbic acid reduces any remaining unbound dianionic chromium 51 to the anionic state which does not penetrate red blood cells; thus in vivo labeling of red blood cells is prevented.

The extent of chromium 51 labeling is influenced by hematocrit values; hematocrits below 35 percent will result in a higher degree of labeling, whereas hematocrits exceeding 45 percent will produce the opposite result. Although the rate of labeling is initially more rapid at 37° C, samples incubated at 37° C and room temperature will show the same degree of chromium 51 labeling after a 30-minute period.

Labeling may also be accomplished by centrifugation and washing techniques which are described in the literature.

The admixture of Sodium Chromate Cr 51 Injection with Bracco A-C-D Solution Modified (Anticoagulant Citrate Dextrose Solution Modified) for use as a stock solution is not recommended. For best results, the whole blood sample should be combined with Bracco A-C-D Solution Modified prior to labeling.

Radiation Dosimetry

The estimated absorbed radiation doses to an average patient (70 kg) following an intravenous injection of 7.40 megabecquerels (200 microcuries) of Cr 51 are shown in Table 4.